Heretofore, in a system for generating hydraulic power, such as a drive apparatus for a hydraulic shovel, by driving a plurality of hydraulic pumps of the variable displacement type by a single internal combustion engine, there have generally been three types of control means for distributing the output power which include:
(a) individual control system; PA1 (b) cross-sensing system; and PA1 (c) full power control system.
The individual control system (a) is such that when for example, two hydraulic pumps are provided one-half the maximum output power of the internal combustion engine is distributed to each of the hydraulic pumps, and the circuit pressure for each hydraulic pump is sensed individually to thereby control the delivery of each pump. A disadvantage of this system, resides in the fact that, when no load is applied to one hydraulic pump, it is impossible for the other hydraulic pump to utilize the residual power.
The cross-sensing system (b) is such that, by enabling two hydraulic pumps to transmit their circuit pressures to each other, one of the pumps can utilize part of the residual power of the other pump when the load applied to the other pump is low. This system is superior to the individual control system in utilization of power, but the regulators for controlling pump delivery are complex in construction.
Meanwhile, the full power control system (c) is such that a reduction in the running speed of the internal combustion engine is sensed to control delivery of the hydraulic pumps, and is regarded as the most excellent system from the view point of utilization of power. One example of this system is proposed in Patent Application Laid-Open No. 4601/75. Although this proposed system is excellent in principle in that a reduction in the running speed of the internal combustion engine is detected and the angle of inclination of the hydraulic pumps is restricted, it is faced with many problems, because the system utilizes hydraulic means for attaining the desired end. However, by utilization of hydraulic means, this system has a low responsiveness and it is susceptible to the influences of variations in oil temperature. Moreover difficulties are encountered in following changes in the running speed set for the internal combustion engine, as well as in maintaining the dynamic stability of the entire system in good condition. Furthermore, the necessary regulators become complex in construction when attempts are made to externally operate the maximum value of the pumps' inclination angle.
An object of this invention is to provide a method of controlling a system for generating hydraulic power, which system includes an internal combustion engine and plurality of hydraulic pumps of the variable displacement type driven thereby, so as to enable a realization of full power control of excellent responsiveness and dynamic stability.
Another object of the invention is to provide a control method the hydraulic power generating system, which enables a realization of full power control which is free from stopping or shut down of the internal combustion engine.
Yet another object of the invention is to provide a control method for the hydraulic power generating system, so as to enabling a realization of full power control which suppress a reduction in output torque in a region of low speed of the internal combustion engine while causing no incomplete combustion, such as production of black smoke in a region of high engine speed.
A further object of the invention is, to provide a method of controlling a system for generating hydraulic power, which system includes an internal combustion engine and at least one hydraulic pump of the variable displacement type driven thereby, to realize a control method in which, when the angle of inclination of the swash plate of the pump is controlled by using a pump control coefficient associated with engine speed deviation, there is no occurence of sudden changes in pump delivery such as a reduction in pump delivery which would occur due to a reduction in the inclination angle in spite of an operation performed to increase the output engine speed, and an increase in pump delivery which would occur due to an increase in the inclination angle in spite of an operation performed to reduce the output engine speed.